Throughout the world, a number of plastic materials are known which, in addition to the plastic material, which is usually substantially organic, also contain mainly inorganic, fibrous or particulate or other foreign substances or have different compositions, which it is desirable to separate during recycling. One well-known example is plastic windows made of polyvinyl chloride material (PVC) which are reinforced by the addition of glass fibres or contain different additives.
Plastic materials, such as PVC, which are free of inorganic, fibrous, particulate or other foreign substances can be recycled in the well-known manner. Established processes for recycling used PVC plastic windows, PVC plastic profiles and corresponding production waste are known in the art.
On the one hand, however, if foreign substances are contained in the plastic material, they can disturb the treatment and recycling process to such an extent that recycling is no longer possible. This is principally due to the fact that a recycling step includes feeding the plastic material into an extruder and filter apparatuses. In the extruder, and also in the filter apparatuses, the foreign substances have a very abrasive effect, which results in very rapid damage to the extruder and the filters.
At the same time, there may be economic reasons and questions of product strategy that require all the formulations of a plastic material, such as PVC for window profiles, to be processed uniformly and jointly for re-use as recycled granules. In the case of glass-fibre-reinforced PVC, all the manufacturers of window profiles who used the recycled granules would have glass fibres in their PVC profiles, even though it is questionable whether that is economically desirable or suitable in terms of product strategy.
There is therefore a need in the art both to detect and to separate plastic materials containing foreign substances from those plastic materials which do not contain any foreign substances at the earliest possible stage at the beginning of a recycling process.
It is therefore an object of the present invention to develop the generic material, preferably plastic material, further in a way which overcomes the disadvantages of the prior art, especially in such a way that detection and screening can as far as possible be performed reliably at the beginning of a recycling process.
It is a further object of the invention to provide a process for sorting a mixture of materials, which mixture contains at least one material in accordance with the invention.
The first object is achieved by a material, preferably a plastic material, comprising foreign substances, characterized in that the material comprises at least one fluorescent compound.
In this context, it is preferable that the foreign substances are fibrous or particulate and are preferably selected from the group consisting of glass fibres, silica and mixtures thereof.
It is also proposed in accordance with the invention that the fluorescent compound comprises Anti-Stokes-crystals or -pigments.
One embodiment is characterised in that the fluorescent compound is blended into the material substantially homogeneously.
It is also preferable that the material is selected from the group consisting of polyvinyl chloride (PVC) and vinyl chloride copolymers.
It is also preferable that the material comprises PVC window frames, PVC profiles, PVC production waste and mixtures thereof.
It is further preferable that the fluorescent compound is present in a concentration of 10-200 ppm based on the total weight of the material.
It is particularly preferable that Anti-Stokes-crystals are present.
Anti-Stokes-crystals are known in the art. They can be excited to fluoresce by electromagnetic radiation. At very specific excitation energies, multi-photon processes can cause the generation of fluorescent radiation whose energy is higher than the excitation energy. With an excitation radiation in the IR range, for example, it is possible to generate visible radiation. For this to happen, the excitation radiation must exactly match the energy transitions of the crystal and must therefore be very narrow-band. If the excitation radiation is outside the effective range, the crystal reacts without fluorescence, or does not light up.
The second object is achieved by a process for sorting a mixture of materials, wherein the mixture comprises at least one inventive material, the process comprising the steps of: i) optionally coarsely and/or finely comminuting the materials, preferably to a size of 0.1-2.0 cm, ii) exciting at least one fluorescent compound in the inventive material; iii) detecting the inventive material containing the excited fluorescent compound; and iv) separating the detected inventive material from the other materials.
It is particularly preferable in this regard that the process is carried out in several stages, wherein different excitation energies are used in each stage in order to excite different fluorescent compounds each time and to screen out the materials containing the respective fluorescent compound.